A. Field of the Invention
The present invention relates to network systems. More specifically, the invention relates to a router apparatus located at a boundary of logical networks and a method for setting up a virtual connection to transfer packets through the router apparatus.
B. Description of the Background Art
It is known to use a router apparatus to connect LANs (local area networks), and transfer packets from one LAN to another LAN. A packet includes source and destination network-layer addresses in addition to communication data. The router apparatus uses the address information to determine an output interface and a next-hop node of the packet.
Such a known router apparatus can perform not only unicast communication in which packets are transferred from a single source to a single destination, but also multicast communication in which packets are sent from a single source to multiple destinations.
In recent years, a technique of resource reservation at the router has been applied when sounds and/or pictures are transferred using packets. Transferring sounds/pictures and other data without this technique results in broken sound and corrupt video. The resource reservation technique is useful not only in transferring sounds/pictures but also in transferring priority data. In order to perform the resource reservation at the router, it is necessary to exchange resource reservation information between nodes such as routers.
One currently developed protocol for the resource reservation technique, RSVP (Resource ReSerVation Protocol), applies to both unicast and multicast. In RSVP, the resource reservation is performed from a destination node to a source node. Specifically, a PATH message is sent from node to node along a path in a direction flowing from the source node to the destination node, and lets routers along this path. store information regarding the path on which the data is to be transferred. This PATH message contains an identifier that specifies the data on which the resource reservation is to be performed and an IP address of the node that sent the PATH message.
When the destination node receives the PATH message, it notifies its request for resource reservation by sending an RESV message upstream, back to the source node in response to the PATH message. This RESV message contains an identifier that specifies the data for which resources are to be reserved and a quality of service (QOS) requested by the destination node.
When a node receives the RESV message, it determines whether its network-layer (e.g., Internet Protocol (IP)) processing unit has sufficient capacity for this resource reservation. If so, the node performs network-layer scheduling to reserve the resources and transfers the RESV message upstream. If not, the node sends an RESV_ERROR message downstream. This procedure is repeated until the RESV message reaches the source node, thereby completing the resource reservation.
A significant problem may arise, however, in such a router apparatus and resource reservation technique. It is often the case that the router has a relatively low capacity in its network-layer processing unit. As such, the reservation of resources sufficient for the requested service quality indicated in the RESV message can seldom be achieved by the network-layer scheduling. Accordingly, a router apparatus and resource reservation technique is needed to avoid this problem.
It is therefore an object of the present invention to provide a scheme for performing resource reservation that avoids limitations in the network-layer processing capacity of the routers, yet correctly reserves resources at a certain router.
Another object of the present invention is to provide a technique for efficiently setting up a virtual connection for multicast communication when a lower-layer switching function is used at a router.
Yet another object of the present invention is to provide a technique for efficiently setting up a virtual connection for multicast communication, while uniquely identifying the connection between neighboring nodes, where a network includes a switch that changes an identifier of the connection between neighboring nodes.
According to one aspect of the present invention, there is provided a router apparatus, comprising a memory capable of storing a correspondence relationship between a first virtual connection to be used in receiving a packet from one logical network and a second virtual connection to be used in transmitting the packet to another logical network; a device for receiving a first message for resource reservation from said another logical network; and a device for transmitting a second message for resource reservation based on the first message received by the device for receiving to said one logical network, responsive to an existence of the first and second virtual connections, the correspondence relationship between the first and second virtual connections being to be stored in the memory.
In another aspect, there is provided a router apparatus, comprising a memory capable of storing a correspondence relationship between a first virtual connection to be used in receiving a packet from one logical network and a second virtual connection to be used in transmitting the packet to another logical network; a device for receiving a first message for resource reservation from said another logical network; a device for transmitting a second message for resource reservation based on the first message received by the device for receiving to said one logical network; and a device for canceling the second message transmitted by the device for transmitting, responsive to an existence of the first and second virtual connections, the correspondence relationship between the first and second virtual connections being to be stored in the memory.
In a further aspect, there is provided a method of operating a router usable to transfer a packet from a first node belonging to one logical network to a second node belonging to another logical network, comprising the steps of receiving a first message for resource reservation from the second node; storing a correspondence relationship between a first virtual connection available for receiving a packet of a specified flow from the first node and a second virtual connection available for transmitting the packet of the specified flow to the second node, when the first and second virtual connections exist; and transmitting a second message for resource reservation based on the first message to the first node, when the correspondence relationship can be stored.
In yet another aspect, there is provided a method of operating a router usable to transfer a packet from a first node belonging to one logical network to a second node belonging to another logical network, comprising the steps of receiving a first message for resource reservation from the second node; transmitting a second message for resource reservation based on the first message to the first node; storing a correspondence relationship between a first virtual connection available for receiving a packet of a specified flow from the first node and a second virtual connection available for transmitting the packet of the specified flow to the second node, when the first and second virtual connections exist; and transmitting a cancellation message to the first node for canceling the second message, depending upon whether or not the correspondence relationship can be stored.
In still a further aspect, there is provided a method of transferring a packet from one logical network to a plurality of nodes belonging to another logical network via a router, a default virtual connection being set up between the router and each of the nodes, comprising the steps of setting up a dedicated virtual connection from the router to at least one of the nodes, the dedicated virtual connection being dedicated for transmitting a packet of a specified flow to the nodes and capable of being a point-to-multipoint connection; transferring the packet of the specified flow received from said one logical network onto the dedicated virtual connection without a network-layer destination analysis; receiving a message through the default virtual connection from one of the nodes; and maintaining the dedicated virtual connection based on receipt of the message.
In an additional aspect, there is provided a method of transferring a packet from one logical network to a plurality of nodes belonging to another logical network via a router, a default virtual connection being set up between the router and each of the nodes, comprising the steps of setting up a dedicated virtual connection from the router to at least one of the nodes, the dedicated virtual connection being dedicated for transmitting a packet of a specified flow to the nodes and capable of being a point-to-multipoint connection; transmitting an identifier of the dedicated virtual connection onto the dedicated virtual connection, the identifier being common between the router and at least one of the nodes; receiving the identifier through the default virtual connection from a corresponding one of the nodes; and transferring the packet of the specified flow received from said one logical network onto the dedicated virtual connection without a network-layer destination analysis.
Other features and advantage of the present invention will be become apparent from the following description taken in conjunction with the accompanying drawings.
Both the foregoing general description and the following detailed description provide examples consistent with this invention and explain how to make and use systems and methods consistent with the invention. These description do not restrict the claimed invention.